The propagation of inverted Neel wall sections instead of magnetic bubbles in a serial access memory system was proposed by L. J. Schwee in the publication "Proposal On Cross-Tie Wall and Bloch-line Propagation In Thin Magnetic Films," IEEE Transactions on Magnetics, MAG 8, No. 3, pages 405 - 407, September 1972. Such a memory system utilizes a ferromagnetic film of 81% Ni - 19% Fe of approximately 300 Angstroms (A) thick in which cross-tie walls can be changed in Neel walls and Neel walls can be changed to cross-tie walls by applying appropriate fields. Associated with the cross-tie walls is a section of inverted Neel wall that is bounded by a cross-tie wall on one end and a Bloch-line on the other end.
In such a cross-tie wall memory system, information is entered at one end of the serial access memory system by the generation of an inverted Neel wall section bounded by a cross-tie on one side and a Bloch-line on the other side that is representative of a stored binary 1 and a non-inverted Neel wall section, i.e., the absence of a cross-tie and Bloch-line pair (that is representative of a stored binary 0, and is moved or propagated along the cross-tie wall by the successive generation) and then the selective annihilation of inverted Neel wall sections at successive memory cells along the cross-tie wall. In the D. S. Lo, et al, U.S. Pat. No. 3,906,466 there is disclosed a propagation circuit for the transfer of inverted Neel wall sections at successive memory cells along the cross-tie wall. In the L. J. Schwee U.S. Pat. No. 3,868,660 and in the publication "Cross-tie Memory Simplified By The Use of Serrated Strips," L. J. Schwee, et al, AIP Conference Proceedings, No. 29, 21st Annual Conference On Magnetism and Magnetic Materials, 1975, published April 1976, pages 624 - 625 there have been published some more recent results of the further development of cross-tie wall memory systems.
In prior art cross-tie wall memory systems, the magnetic film that functions as the storage medium has the property of uniaxial anisotropy with an easy axis, which easy axis is generated in the magnetic film during its generation in the vapor deposition process. This magnetic field induced anisotropy constrains the generation of the cross-tie wall along and parallel to the easy axis. In the above L. J. Schwee, et al, AIP publication there are proposed serrated strips of Permalloy film, about 350 Angstroms (A) in thickness and 10 microns (.mu.m) in width, which serrated strips are etched from a planar layer of the magneti material so that the strips are aligned along the easy axis of the film. After an external magnetic field is applied normal to the strip length, i.e., transverse the easy axis of the film, the magnetization along the opposing serrated edges rotates back to the nearest direction that is parallel to the edge. This generates two large domains that are separated by a wall that is formed along the center line of the strip. This wall may have cross-ties. Cross-ties are formed at the necks of the serrated edges while Bloch-lines are formed in the potential wells between adjacent necks.
This serrated strip configuration, because of the contour of the opposing edges of the strip, provides the means whereby the cross-tie, Bloch-line pairs are structured at predetermined memory sections along the strip. However, because the prior art strips have field induced uniaxial anisotropy imparted during deposition, such strips cannot be utilized to permit the use of nonlinear, i.e., curved, data tracks, which curved data tracks are essential to the configuration of cross-tie wall memory systems of large capacity or of digital logic function capabilities. Accordingly, it is desirable that there be provided a means whereby cross-tie wall memory systems use nonlinear, i.e., curved, data tracks to achieve the desirable characteristics of single wall, e.g., bubble, domain memory systems, such as those of the A. H. Bobeck, U.S. Pat. No. 3,729,726 and the D. M. Heinz, U.S. Pat. No. 3,735,145, in cross-tie wall memory systems.
In the copending M. C. Paul, et al, patent application No. 756,224 filed Jan. 3, 1977, there is disclosed a cross-tie wall memory system and in particular a data track therefor that is formed of a strip of magnetic material having substantially zero magnetic field induced anisotropy. The data-track-defining-strip of isotropic magnetic film utilizes its shape, i.e., its edge contour induced, anisotropy to constrain the cross-tie wall within the planar contour and along the centerline of the film strip. Accordingly, the cross-tie wall is constrained to follow the path defined by the magnetic film strip which path may be configured into a major loop, or circular data track, configuration for large capacity memory storage.